Dynamic decompression control for high pressure seals

ABSTRACT

The present disclosure is directed to a method and system for dynamically controlling seal decompression. The method includes monitoring a set of parameters associated with an operation of a seal, wherein the set of parameters includes a maximum pressure subjected to the seal and an exposure time at the maximum pressure, calculating a target pressure ramp down rate based on at least one of the maximum pressure and the exposure time, and decreasing a pressure about the seal at a decompression rate that is based on the target pressure ramp down rate. The system includes a controller having a memory device, a graphical user interface, at least one pressure transmitter configured to monitor the pressure about the seal, and a processor, wherein the processor is configured to detect a maximum exposure pressure and exposure time at maximum pressure about the seal and control a pressure ramp down about the seal based on the maximum exposure pressure and the exposure time detected in order to prevent explosive decompression of the seal.

This application is a continuation application of U.S. patentapplication Ser. No. 14/334,772, filed on Jul. 18, 2014, which claimspriority to U.S. Provisional Patent Application No. 61/857,281, filed onJul. 23, 2013, the entire contents of which are incorporated herein byreference.

The present disclosure is directed towards seals operating at highpressure in a hydrogen environment, and more specifically, todynamically controlling decompression of high pressure seals.

Seals are devices designed to join components or mechanisms to togetherby preventing leakage, containing pressure, or excluding contamination.Seals come in a variety of configurations. For example, a seal can takethe form of a flange gasket, o-ring, hose coupling, etc. Seals also comein a variety of materials, for example, synthetic rubbers such as butyl,polytetrafluoroethylene (PTFE), polyisoprene, silicone or thermoplasticssuch as elastomer, polyurethane, or polyamide.

Seal failure can occur for a variety of reasons depending on the seal,application, environment, and fluid in contact with the seal. Forexample, one particular mechanism for seal failure when handling a smallmolecule gas (e.g. hydrogen) is the failure of seal materials due toexplosive decompression. Explosive decompression can be caused by asudden decrease in pressure, which results in the sudden expansion ofgas trapped within the seal structure as the surrounding pressuredecreases. Due to the relatively slow rates of diffusion for hydrogen insolid materials (e.g., polymeric and elastomeric), when the surroundingpressure changes at a rate faster than the trapped gas can escape, gaspockets can form inside the material, which can tear apart the materialfrom the inside out.

A particular application where explosive decompression presents achallenge is in high pressure electrochemical cells utilizing hydrogen.Electrochemical cells usually classified as fuel cells or electrolysiscells, are devices used for generating current from chemical reactions,or inducing a chemical reaction using a flow of current. For example, afuel cell converts the chemical energy of a fuel (e.g., hydrogen,natural gas, methanol, gasoline, etc.) and an oxidant (air or oxygen)into electricity and waste products of heat and water.

The basic technology of a hydrogen fuel cell can be applied toelectrochemical hydrogen manipulation, such as, electrochemical hydrogencompression, purification, or expansion. An electrochemical hydrogencompressor (EHC), for example, can be used to selectively transferhydrogen from one side of a cell to another. EHCs operating in thismanner are sometimes referred to as a hydrogen pumps. When the hydrogenaccumulated is restricted to a confined space, the electrochemical cellcompresses the hydrogen. In some case a hydrogen compressor can compresshydrogen to pressures up to or exceeding 15,000 psi. The maximumpressure or flow rate an individual cell is capable of producing can bebased on the cell design.

Electrochemical hydrogen manipulation has emerged as a viablealternative to the mechanical systems traditionally used for hydrogenmanagement. Successful commercialization of hydrogen as an energycarrier and the long-term sustainability of a “hydrogen economy” dependslargely on the efficiency, safety, and cost-effectiveness of fuel cells,electrolysis cells, and other hydrogen manipulation/management systems(i.e., EHCs). Gaseous hydrogen is a convenient and common form forenergy storage, usually by pressurized containment. Advantageously,storing hydrogen at high pressure yields high energy density. Therefore,there is a need to address the issue of explosive decompression,particularly with regard to high pressure electrochemical cells.

One proposed solution to this issue of explosive decompression for highpressure electrochemical cell applications is decompressing theelectrochemical stack or cell at a fixed rate slower than the rate atwhich the hydrogen can leak from the material. However, this limits thepotential response time of the system in situations where the rate istoo conservative.

In consideration of the aforementioned circumstances, the presentdisclosure is directed to a dynamic decompression control method andsystem for high pressure seals.

One embodiment of the present disclosure is directed to a method ofdynamically controlling seal decompression. The method comprisesmonitoring a set of parameters associated with an operation of a seal,wherein the set of parameters includes a maximum pressure subjected tothe seal and an exposure time at the maximum pressure, calculating atarget pressure ramp down rate based on at least one of the maximumpressure and the exposure time, and decreasing a pressure about the sealat a decompression rate that is based on the target pressure ramp downrate.

In another embodiment, the calculation of the target pressure ramp downrate is further based on the seal material of construction. In anotherembodiment, the set of parameters further comprises gas source, hydrogenpartial pressure in the gas source, temperature, humidity and seal age.In another embodiment, at least a portion of the seal is formed of EPDM,Viton, nylon, valox, polycarbonate, silicone, polyethylene,polypropylene, polyurethane, polyethylene terephthalate, andpolyethylene naphthalate. In another embodiment, the environment aboutthe seal contains hydrogen.

Another embodiment of the present disclosure is directed to a method ofdynamically controlling decompression for an electrochemical stack. Themethod comprises detecting a maximum exposure pressure and an exposuretime at maximum pressure for the electrochemical stack and controllingthe pressure ramp down of the electrochemical stack based on the maximumexposure pressure and the exposure time detected in order to preventexplosive decompression of the electrochemical stack.

In another embodiment, controlling decompression of the electrochemicalstack is further based on the electrochemical stack materials ofconstruction. In another embodiment, the electrochemical stack includesseals formed of EPDM, Viton, nylon, valox, polycarbonate, silicone,polyethylene, polypropylene, polyurethane, polyethylene terephthalate,and polyethylene naphthalate. In another embodiment, the electrochemicalstack gas source is hydrogen.

Another embodiment of the present disclosure is directed to a system fordynamically controlling decompression for an electrochemical stack. Thesystem comprising an electrochemical stack and a controller, wherein thecontroller is configured to detect maximum exposure pressure andexposure time at maximum pressure for the electrochemical stack andcontrol a pressure ramp down of the electrochemical stack based on themaximum exposure pressure and the exposure time detected in order toprevent explosive decompression of the electrochemical stack.

In another embodiment, the control of the pressure ramp down is furtherbased on the electrochemical stack materials of construction. In anotherembodiment, the electrochemical stack is configured to operate atoperating pressure ranging from about 0 psi to about 15,000 psi.

Another embodiment of the present disclosure is directed to a system fordynamically controlling seal decompression. The system comprising acontroller comprising a memory device, a graphical user interface, atleast one pressure transmitter configured to monitor the pressure aboutthe seal, and a processor, wherein the processor is configured to detecta maximum exposure pressure and exposure time at maximum pressure aboutthe seal and control a pressure ramp down about the seal based on themaximum exposure pressure and the exposure time detected in order toprevent explosive decompression of the seal.

In another embodiment, the control of the pressure ramp down is furtherbased on the seal material of construction. In another embodiment, theenvironment about the seal contains hydrogen.

Another embodiment of the present disclosure is directed to a method ofdynamically controlling seal decompression by executing an integratingfunction to accumulate a total exposure time at time-varying pressurelevels for the seal, wherein a target ramp down rate can be calculatedbased on a pressure-weighted function.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a schematic view of part of an electrochemical stack system,according to an exemplary embodiment.

FIG. 2 is a schematic view of part of a controller, according to anexemplary embodiment.

FIG. 3 is a chart of pressure vs. time showing various decompressionscenarios, according to an exemplary embodiment.

FIG. 4 is a chart of pressure vs. time showing various decompressionscenarios, according to an exemplary embodiment.

FIG. 5 is a chart of pressure vs. time showing various decompressionscenarios, according to an exemplary embodiment.

FIG. 6 is a chart of pressure vs. time showing various decompressionscenarios, according to various embodiments.

FIG. 7 is a flow chart showing a decompression control method, accordingto an exemplary embodiment.

Reference will now be made in detail to the present exemplaryembodiments of the present disclosure, examples of which are illustratedin the accompanying drawings. Wherever possible, the same referencenumbers will be used throughout the drawings to refer to the same orlike parts. Although described in relation to electrochemical cells andstacks employing hydrogen, it is understood that the methods and systemsof the present disclosure can be employed with various types ofpressurized sealed systems.

FIG. 1 shows a portion of an electrochemical stack system 100, accordingto an exemplary embodiment. The electrochemical stack system 100 cancomprise an electrochemical stack 110 and a controller 120 incommunication with electrochemical stack 110. As shown in FIG. 1,electrochemical stack 110 can be comprised of multiple electrochemicalcells 111 stacked adjacent to one another to form electrochemical stack110. Controller 120 can be configured to be separate from stack 110 asshown in FIG. 1 or according to various other embodiments controller 120can be configured to be integrated within stack 110. In otherembodiments, controller 120 can be configured to communicate and controla plurality of electrochemical stacks.

In operation, according to an exemplary embodiment, hydrogen gas can besupplied to electrochemical stack 110 and distributed to eachelectrochemical cell 111. An electric potential can be applied and thehydrogen within each electrochemical cell 111 can be oxidized causingthe hydrogen to split into electrons and protons. The protons areelectrochemically transported through a proton exchange membrane (notshown) within each electrochemical cell 111 while the electrons arererouted around. At the opposite side the proton exchange membranetransported protons and rerouted electrons are reduced to form hydrogen.As more and more hydrogen is formed at the opposite side the hydrogencan be compressed and pressurized within a confined space.

Within each electrochemical cell 111 and within electrochemical stack110, a plurality of high pressure zones and a plurality of seals candefine the plurality of pressure zones. The components (e.g., plates,seals, etc.) acting as the boundary to each pressure zone can be exposedto the hydrogen gas at varying pressure. For example, the pressurewithin electrochemical stack 110 can range from about 0 psi to about15,000 psi.

In operation, at least a portion of the hydrogen gas exerting force dueto pressure on the seals can diffuse into the seal material (e.g.,polymers and elastomers). The quantity of hydrogen that diffuses intothe seal material can be based on the hydrogen pressure being exerted onthe seals and the period of exposure. There can be a period of time atwhich a seal can be saturated for a given pressure and diffusion ofhydrogen into the seal material will stop. This saturation time, whichcan be dependent on the hydrogen pressure, can be referred to ast_(max). According to the various embodiments, the materials ofconstruction can be considered in determining the saturation timet_(max). In addition, the seal geometry (e.g., thickness) can affect thesaturation time t_(max). The saturation time t_(max) can be a combinedfunction of the geometry and diffusivity of the material ofconstruction.

Electrochemical stack 110 can operate at different pressures fordifferent durations depending on various factors, for example,application, load requirements, etc. The pressure within electrochemicalstack 110 may decrease for various reasons, for example, a change inoperating parameters or as part of a shutdown. For an emergencyshutdown, the pressure can vary from operating pressure to ambient forsafety and servicing reasons. Under normal operating conditions theoutlet of electrochemical stack 110 can be exposed to various pressurelevels in storage vessels.

Ramping down the pressure within electrochemical stack 110 at a ratefaster than the hydrogen gas can diffuse out of the seal material cancause gas pockets to form internal to the seal structure. Consequently,as the external hydrogen pressure decreases the volume of the gaspockets increases producing high internal stress, which can cause theseal to deform and be torn apart (i.e., explosive decompression).

To reduce the potential for explosive decompression, the rate ofdecompression (i.e., the pressure ramp down rate) within electrochemicalcell 110 can be controlled to limit the formation of gas pocketsinternal to the seal material and maintain low internal stress.Controlling the pressure ramp down rate can include reducing thepressure of the hydrogen gas within electrochemical stack 110 at a rateslow enough to allow the hydrogen that diffused into the seal materialto diffuse back out of the seal as a result of the pressure differentialwithout forming gas pockets and high internal stress within the seal.

As briefly discussed above, the pressure ramp down rate can becontrolled to a fixed rate of decompression based on a given scenario.For example, the fixed rate of decompression can be calculated based onthe worst case scenario, which would be the maximum operating pressureof the electrochemical stack and an exposure time of t_(max).Calculating the fixed rate of decompression based on the worst casescenario can ensure that the decompression will be sufficiently slowregardless of the operating pressure or the time of exposure. However,controlling based on the worst case scenario can result in inefficiencydue an overly conservative ramp down time when the electrochemical cellis operating at less than maximum operating pressure or maximum exposuretime.

Alternatively, calculating the fixed rate of decompression based onaverage operating pressure and exposure time can still create situationswhere explosive decompression may occur. Therefore, because responsetime of an electrochemical stack can be an important factor inoperation, performance, and efficiency of the stack it can beadvantageous to dynamically control the decompression of theelectrochemical stack in real time. For example, a ramp down time for anelectrochemical stack operating at a pressure of about 15,000 psi to 0psi might be about 30 minutes controlling based on a fixed ramp downrate at worst case scenario. By dynamically controlling pressure, timecan be reduced to less than about 5 minutes in a situation where theexposure time at about 15,000 psi is relatively short.

Electrochemical stack system 100, according to the present embodimentcan be configured to dynamically control decompression ofelectrochemical stack 110 by calculating the pressure ramp down ratebased on the time-history of the electrochemical stack prior toinitiating a decompression transition. Controller 120 can be configuredto monitor the time-history parameters and use the parameters tocalculate a target pressure ramp down rate in real time upon theinitiation of a decompression transition. The parameters monitored caninclude the maximum pressure, the time spent at that pressure and thematerial(s) of construction for the seal(s). Controller 120 can beconfigured to use one or more parameters to calculate a ramp down ratebased on the time-dependent sum of exposed pressure multiplied byexposure time, with a weighting factor included.

FIG. 2 shows a schematic diagram of controller 120, according to anexemplary embodiment. Controller 120 as shown in FIGS. 1 and 2 can beconfigured to interface with any pressurized device having seals thatundergo decompression.

As shown in FIG. 2, controller 120 can comprise at least one pressuretransmitter 130 or other comparable device configured to read theinternal pressure of a pressurized device 200. In addition, controller120 can be in communication with pressurized device 200 and configuredto perform the decompression of pressurized device 200 at the targetpressure ramp down rate by controlling the inlet and outlet flow forpressurized device 200. The flow can be controlled by the use of valvesor other fluid handling components (not shown).

Pressure transmitter 130 can be comprised of one or more pressuretransmitters configured to monitor the pressure within at least onepressurized zone within pressurized device 200. For example, pressuretransmitter 130 can be configured to monitor the overall pressure ofstack 110 or can be configured to monitor the pressure within eachindividual electrochemical cell 111.

In addition to pressure transmitter 130, controller 120 can be comprisedof a processor 121, memory device 122, and a graphical user interface(GUI) 123. Controller 120 can be configured to monitor and record theparameters at a set interval, for example, every 1 min, 30 seconds, 15seconds, 5 seconds, 1 second, 0.5 seconds, or 0.1 seconds. In addition,controller 120 can be configured to continuously calculate the targetramp down rate based on the most recent parameters. According to anexemplary embodiment, the target ramp down rate can be designed tobalance the potential for explosive decompression and excessive rampdown time. GUI 123 can be configured to allow the user to inputparameters, for example, the seal material, operating pressure range,PID loop parameters, gas source, seal model, seal geometry, safetyfactor, etc.

In an alternate embodiment, controller 120 rather than calculating thepressure ramp down rate based on the parameters monitored can utilize alookup table or database. The lookup table or database can havepre-calculated values for the pressure ramp down rate based on the fullrange of possible operating pressures, time spent at pressure, and sealsmaterials of construction.

EXAMPLE 1

FIG. 3 shows a chart of pressure vs. time illustrating variousdecompression scenarios for electrochemical stack 110. The scenarios canbe separated into two different pressure levels, P_(A) and P_(B).Pressure level P_(B) is shown as a dotted line and pressure level P_(A)is shown as a solid line. FIG. 3 illustrates how the ramp down rate rcan vary based on maximum operating pressure and exposure time atmaximum operating pressure. For the scenarios shown in FIG. 3, the sealsmaterials of construction are assumed to be the same for all thescenarios.

As shown in FIG. 3, the pressure within electrochemical stack 110 canramp up at different rates as illustrated by the different slopes ofP_(A) and P_(B). The pressure for both P_(A) and P_(B) ramps up untilthe pressure levels off. As shown in FIG. 3, the pressure for P_(B) isgreater than P_(A).

Following the pressure leveling off, three different ramp down scenariosare illustrated with regard to P_(A). The first ramp down scenariooccurs when ramp down begins after a duration of t₁ at a ramp down rateof r₁, the second ramp down scenario occurs when ramp down begins aftera duration of t₂ at a ramp down rate of r₂, and the third ramp downscenario occurs when ramp down begins after a duration of t₃ at a rampdown rate of r₃. The ramp down rate is equal to the slope of the rampdown line (ΔP/Δt).

As shown in FIG. 3, exposure time t₃ is greater than exposure time t₂and exposure time t₂ is greater than exposure time t₁. Accordingly,because for each scenario the maximum pressure is the same, the rampdown rate can vary based on exposure time. Therefore, because t₁ is theshortest exposure duration the least amount of hydrogen should have beendiffused into the seal material, in which case ramp down rate r₁ can begreater than ramp down rate r₂ and ramp down rate r₂ can be greater thanramp down rate r₃

Similarly, as shown in FIG. 3, for pressure level P_(B), exposure timet₅ is greater than exposure time t₄. Accordingly, ramp down rate r₄ canbe greater than ramp down rate r₅. In addition, because P_(B) is greaterthan P_(A), if t₅ is equal to t₃ then r₃ can be greater than or equal tor₅. Generally, the rate of decompression can be inversely proportionalto the time spent at maximum pressure and inversely proportional to themaximum exposed pressure level. It is contemplated that theproportionality for the exposed pressure level can be non-linear.

EXAMPLE 2

FIG. 4 shows a chart of pressure vs. time illustrating threedecompression scenarios for electrochemical stack 110. FIG. 4 is similarto FIG. 3, except that FIG. 4 only shows pressure level P_(A) and inFIG. 4 t₂ and t₃ exceed the saturation time t_(max). Therefore, r₂ andr₃ are equal assuming the same materials of construction because thesaturation time is used as the exposure time for both and the maximumpressure is the same.

EXAMPLE 3

In contrast, FIG. 5 shows a chart of pressure vs. time illustrating twodecompression scenarios where the material of construction forelectrochemical stack 110 is different. In both scenarios the exposuretime at maximum pressure is equal to t₁ and t₁ is greater than thesaturation time t_(max). In addition, the maximum pressure is equal forboth scenarios. Therefore, the difference between the two scenarios canbe the material of construction of the boundary components. Scenario 1can be represented by the solid ramp down line which has a slope r₁.Scenario 2 can be represented by the dotted ramp down line which has aslope of r₂ Based on FIG. 5, the material of electrochemical stack 110for scenario 1 has a greater rate of hydrogen diffusion from the sealthan the seal of electrochemical stack 110 for scenario 2. Because ofthe higher rate of hydrogen diffusion for scenario 1 the ramp down rater₁ can be greater than r₂ and as a result response time can be less, asillustrated in FIG. 5.

EXAMPLE 4

In another embodiment, as shown in FIG. 6, the ramp down can be executedin a plurality of steps rather than a steady gradual decline as shown inFIGS. 3-5. As shown in FIG. 6, the pressure drops down and thensubstantially stabilizes before dropping down again. The overall rate ofdecompression for the plurality of step downs can be substantially equalto the overall rate of decompression for the steady ramp down.

In another embodiment, the ramp down rate can be non-linear (e.g.,exponential, logarithmic, polynomial). For example, the ramp down ratecan be slower at higher pressure and as the pressure decreases the rampdown rate can increase exponentially.

In various embodiments, additional parameters can be monitored andfactored into the calculation of the ramp down rate. For example, thegas source, the partial pressure of hydrogen in the gas source, thetemperature, the humidity, and the seal age.

In various other embodiments, it is contemplated that the ramp down ratecan be recalculated and the ramp down rate can be adjusted uponinitiation of the decompression as well as throughout a decompression.

FIG. 7 is a flow chart illustrating the various steps of a method ofdynamically controlling the decompression for high pressure seals,according to an exemplary embodiment. The method comprises monitoring aset of parameters associated with an operation of a seal. The set ofparameters can include the maximum pressure subjected to the seal andthe exposure time at the maximum pressure. Once a decompressiontransition is triggered calculation of the target pressure ramp downrate based on at least one of the maximum pressure and the exposure timecan be executed. Then decompression (i.e., decreasing of the pressure)can commence at a decompression rate that is determined based on thetarget ramp down rate. According to various embodiments, thedecompression rate may be equal to the target ramp down rate or thedecompression rate may vary from the target ramp down rate by, forexample, about +/−1%, 5%, 10%, 20%, 30%, 40%, 50%, or greater than 50%.

According to various embodiments, during the decompression theparameters can be continuously monitored and the target ramp down ratecan be updated to provide feedback loop control.

In another embodiment, controller 120 can be configured to perform anintegrating function. This function can accumulate the total exposuretime at time-varying pressure levels. The ramp down rate can becalculated based on a pressure weighted function. For example, the rampdown rate can be the integral of P*d(t). In yet another embodiment,controller 120 ramp down control can be configured to operate above acertain pressure threshold. For example, controller 120 can startcalculating the ramp down rate when pressure within the electrochemicalcell rises above about 100 psi, 500 psi, 1,000 psi, 5,000 psi, 10,000psi, or 15,000 psi.

According to the various embodiments, controlling the ramp down rate cansubstantially limit or prevent “explosive decompression” to seals inhigh pressure devices. One particular embodiment is controlling the rampdown rate for electrochemical stacks, which seals can be susceptible todamage from explosive decompression. The seals for an electrochemicalstack can be formed from any elastomeric or polymeric material,including, but not limited to, EPDM, Viton, nylon, valox, polycarbonate,silicone, polyethylene, polypropylene, polyurethane, polyethyleneterephthalate, and polyethylene naphthalate.

Other embodiments of the present disclosure will be apparent to thoseskilled in the art from consideration of the specification and practiceof the present disclosure herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the present disclosure being indicated by the followingclaims.

What is claimed is:
 1. A system for dynamically controllingdecompression for an electrochemical cell comprising: an electrochemicalcell; and a controller, wherein the controller is configured to detectmaximum exposure pressure and exposure time at maximum pressure for aseal of the electrochemical cell and control a pressure ramp down of theelectrochemical cell based on the maximum exposure pressure and theexposure time detected in order to prevent explosive decompression ofthe seal.
 2. The system of claim 1, wherein the control of the pressureramp down is further based on the materials of construction of the seal.3. The system of claim 2, wherein at least a portion of the materials ofconstruction of the seal includes EPDM, Viton, nylon, valox,polycarbonate, silicone, polyethylene, polypropylene, polyurethane,polyethylene terephthalate, and/or polyethylene naphthalate.
 4. Thesystem of claim 1, wherein the control of pressure ramp down is furtherbased on at least one of a gas source supplying the electrochemicalstack, hydrogen partial pressure in the gas source, temperature of thegas source, humidity in the gas source, the seal thickness, the sealgeometry, and/or the seal age.
 5. The system of claim 1, wherein theelectrochemical cell is configured to operate at an operating pressureranging from about 0 psi to about 15,000 psi.
 6. The system of claim 3,wherein the environment about the seal contains hydrogen.
 7. A systemfor dynamically controlling seal decompression of a seal located in apressurized environment, the system comprising: a controller comprising:a memory device, a graphical user interface, at least one pressuretransmitter configured to monitor the pressure about the seal, and aprocessor; wherein the processor is configured to detect a maximumexposure pressure and exposure time at maximum pressure about the sealand control a pressure ramp down about the seal based on the maximumexposure pressure and the exposure time detected in order to preventexplosive decompression of the seal.
 8. The system of claim 7, whereinthe control of the pressure ramp down is further based on the materialof construction of the seal.
 9. The system of claim 8, wherein at leasta portion of the material of construction of the seal is formed of EPDM,Viton, nylon, valox, polycarbonate, silicone, polyethylene,polypropylene, polyurethane, polyethylene terephthalate, and/orpolyethylene naphthalate.
 10. The system of claim 7, wherein the controlof the pressure ramp down is further based on at least one of a gassource supplying the pressurized environment, hydrogen partial pressurein the gas source, temperature of the gas source, humidity in the gassource, the seal thickness, the seal geometry, and/or the seal age. 11.The system of claim 7, wherein the pressurized environment about theseal contains hydrogen.